1. Field of the Invention
The present invention relates to a germ-removing filter for sterilizing air to be supplied into a sterile room (bioclean room) used in e.g. manufacture of food products, medical products, breeding and/or germ-free experiments of laboratory animals, in particular a sterile room in a hospital and relates also to an apparatus using the germ-removing filter for maintaining the sterile room under the sterile condition.
2. Description of the Related Art
The convention has proposed following means for maintaining a sterile room under a sterile condition;
According to the first method, living germs as a kind of fine particles are removed together with dust by a HEPA filter (high performance filter) and also a chemical sterilizing treatment such as a fumigation is effected on the sterile room periodically or non-periodically. In short, the HEPA filter is utilized as a germ-removing filter.
According to the second method, as a HEPA filter to be incorporated within an air supply passage extending to a sterile room, there is used a HEPA filter provided with antimicrobial property by mixing silver zeolite particles as antimicrobial material to a filter substrate at more than 5 g per 1 m.sup.2 of filtering area. This filter is rendered antimicrobial by uniformly mixing silver zeolite particles and binder in the filter substrate in the paper making process of the filter substrate.
According to the third method, as a HEPA filter to be incorporated within an air supply passage extending to a sterile room, there are used threads woven with uniformly mixing silver zeolite particles in synthetic resin fiber. More particularly, this filter uses, as the filter substrate thereof, a non-woven fabric which is formed by causing silver zeolite particles to be uniformly dispersed in a fiber-forming bath of synthetic fiber.
The above-described conventional methods suffer problems to be described next.
The first method inevitably invites formation of pores in the HEPA filter. Thus, the filter is unreliable in its germ-removing effect. Accordingly, for reliably maintaining the sterile room under sterile condition, this method additionally requires the chemical sterilizing treatment using a chemical sterilizing agent. Further, as the sterilizing effect depends mainly on this chemical treatment, it is impossible for this method to achieve complete sterile condition.
In addition, although the living germs may be entrapped within the HEPA filter, these entrapped living germs are stuck within the filter and may proliferate rapidly here due to e.g. variation in humidity. And, these proliferated germs are quite likely to invade the exit or transmission side of the filter through the pores.
In summary, in the case of the first method, although a HEPA filter is employed as a germ-removing filter, this filter is poor in its germ removing performance, so that the sterile room cannot be maintained under sterile condition.
In the case of the second method, since the silver zeolite particles mixed in the filter substrate are very fine particles ranging in diameter about 2 .mu.m on the average, the very presence of such super fine particles within the filter substrate may be detrimental to the original, fine-particle entrapping function of the HEPA filter.
Moreover, the silver zeolite fine particles dispersed and stuck to the surface of the filter substrate via the binder will inevitably fall out therefrom. Hence, there is very high possibility of dust generation due to such fallout of silver zeolite particles. For this reason, the chances are high for the significant deterioration in the original function of the HEPA filter and the deterioration is also inevitable in the antimicrobial effect with passage of time.
On the other hand, if a greater amount of binder were used in order to restrict fallout of the silver zeolite particles, the possibility would increase that the binder would cover the silver zeolite particles entirely. As a result, the method will not be able to provide the filter with the intended antimicrobial effect in spite of the addition thereto of the silver zeolite particles.
In short, with the second method, although this method intends to improve the germ-removing effect through prevention of proliferation of germs within the HEPA filter by providing this filter with the antimicrobial property, this filter cannot provide the antimicrobial effect in a reliable manner. So that, the germs inevitably leak to the transmission side of the filter, and therefore, this method too cannot provide satisfactory germ-removing effect.
In the case of the third method, the silver zeolite particles employed comprise fine particles ranging in diameter about 2 .mu.m on the average as described hereinbefore. On the other hand, the synthetic fiber filament, into which the silver zeolite particles are mixed, have the diameter of 8-15 .mu.m. Accordingly, the possibility is rather low for the entire silver zeolite particles to come out on the surface of the synthetic fiber filament. As a result, this filter can only provide rather limited antimicrobial effect, considering the amount of the silver zeolite particles mixed into the filter substrate. Moreover, there is significant irregularity in the amount of the silver zeolite particles coming out to the surface of the synthetic fiber filament. Accordingly, with this filter, it is difficult to obtain stable antimicrobial effect.
In conclusion, with this third method too, although the method intends to improve the germ-removing effect through prevention of proliferation of germs within the HEPA filter by providing this filter with the antimicrobial property, this filter cannot provide the antimicrobial effect in a reliable manner. So that, the germs inevitably leak to the transmission side of the filter, and therefore, this method too cannot provide satisfactory germ-removing effect.
In view of the above-described state of the art, a first object of the present invention is to provide a germ-removing filter which can remove germs reliably.
A second object of the invention is to provide a germ-removing filter which can provide improved germ-entrapping rate, in addition to the improved reliability.
A third object of the invention is to effectively utilize the above-described, germ-removing filter to prevent invasion of living germs into a sterile room through an air supply passage or an air exhaust passage extending to the sterile room.
A fourth object of the invention is to effectively utilize the above-described, germ-removing filter to prevent invasion of living germs into a sterile room through an air supply passage extending thereto in a system where the air supply passage incorporates therein a HEPA filter for filtering the air to be supplied to the sterile room.